Brooke has to set up 70 chairs in equal rows for the class talent show. but, there is not room for more than 20 rows. what are the possible number of rows that brooke could set up

The answer is 2, 5, 7, 10, and 14.

Let x be the number of rows. There is not room for more than 20 rows:
x ≤ 20

Since all rows must be equal, when we divide 70 by x, we must get a whole number. So, we must find all divisors of 70 smaller or equal to 20 and they are: 2, 5, 7, 10, and 14.
So, the possibilities are:
2 rows with 35 chairs in each row
5 rows with 14 chairs in each row
7 rows with 10 chairs in each row
10 rows with 7 chairs in each row
14 rows with 5 chairs in each row

Are you trying to figure out the volume?